Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use thermal, electrostatic, or piezoelectric technology.
Piezoelectric ink jet print heads include an array of piezoelectric elements (i.e., transducers, PZTs, or actuators) overlying an ink-filled body chamber. Piezoelectric ink jet print heads can typically further include a flexible diaphragm or membrane to which the array of piezoelectric elements is attached. When a voltage is applied to a piezoelectric element, typically through electrical connection with a top electrode electrically coupled to a power source, the piezoelectric element bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle or jet. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
In electrostatic ejection, each electrostatic actuator, which is formed on a substrate assembly, typically includes a flexible diaphragm or membrane, an ink-filled ink chamber between the aperture plate and the membrane, and an air-filled air chamber between the actuator membrane and the substrate assembly. An electrostatic actuator further includes an actuator top electrode formed on the substrate assembly. When a voltage is applied to activate the actuator top electrode, the membrane is drawn toward the top electrode by an electric field and actuates from a relaxed state to a flexed state, which increases a volume of the ink chamber and draws ink into the ink chamber from an ink supply or reservoir. When the voltage is removed to deactivate the actuator top electrode, the membrane relaxes, the volume within the ink chamber decreases, and ink is ejected from the nozzle in the aperture plate.
Some printheads include the use of a bulk piezoelectric material that is from 2 to 4 mils (50 to 100 μm) thick and a stainless steel diaphragm that is 20 microns or more in thickness. The diaphragm of these printheads overlies a body chamber that may be square or trapezoidal in shape, where the body chamber has chamber dimensions on the order of 400 to 800 microns per side. These systems typically have low aspect ratio body chambers where the ratio of the length to the width is between 1.0 and 1.5. Other thin film piezoelectric systems include the use of a much thinner diaphragm, on the order of between 1.0 and 5.0 microns thick, or between 1.0 and 3.0 microns thick. Because of the increased flexibility of this thinner diaphragm material, the body chambers of thin film piezoelectric systems may be designed to be a long, thin rectangular shape with a high aspect ratio to control the vibrational modes of the diaphragm that overlies the body chamber. For example, each body chamber may be less than 100 microns wide and more than 600 microns long. These designs may incorporate a top electrode over each body chamber that is similarly long and thin. The top electrode is separated from a bottom electrode by the thin film piezoelectric material. Forming a square or trapezoidal body chamber using a thin diaphragm material would result in a diaphragm that deflects with excessive amplitude or has undesirable vibrational modes during ejection of ink from the nozzle, and the jetting of ink would not be easily controlled. Thin film devices that use a high aspect ratio body chamber typically have arrays of very closely spaced nozzles. When the nozzles are very closely spaced the fluid path is often constructed using a silicon structure and microfabrication methods that can be cost effective in very large build volumes, but are not very cost effective in lower build volumes. A thin-film piezoelectric driver system that can be used in a high density printhead design with a nozzle spacing that enables lower cost manufacturing methods would be desirable.